Purification device for gases

ABSTRACT

An exhaust gas purification device includes a porous body of catalytic material of the general formula A a B b O 4  disposed in an exhaust gas stream of an engine. The porous body of catalytic material has a characteristic response temperature above which it is catalytically active to reduce pollutants in the presence of a reducing agent. The porous body stores at least 20% by volume hydrocarbons at temperatures below the response temperature. A represent at least one element selected from Mg, Ca, Mn, Fe, Ni, Co, Cu, Zn, Sn, Ti and A+B is less than 3, A is greater than 0 and B greater than 0.

This application is a division of application Ser. No. 08/764,465 filedDec. 12, 1996 now U.S. Pat. No. 6,027,703.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method for operating a purificationdevice for gases, especially for exhaust gases of stoichiometricallyoperated gasoline engines, wherein a filter body comprising a catalystis exposed to a gas stream to catalytically convert pollutants, as wellas to a purification device for gases comprising a filter body whichcomprises a catalyst, particularly for stoichiometrically operatedgasoline engines, wherein the filter body is disposed in the exhaust gasstream of an engine, wherein both the method and the purification deviceare useful in the automobile industry.

In the past, to improve the cold-running properties and, in particular,to reduce hydrocarbon emission in the exhaust gases of motor vehicleswith a controlled exhaust gas catalyst, the catalyst was generallyheated in the starting phase. This requires additional energy and anincreased weight. Moreover, such a purification device is expensive anddifficult to recycle because of the catalysts used, such as noble metalsand the like.

Published German Patent 44 20 932 discloses a catalyst for an exhaustgas purification device. This catalyst is made of a spinel or aspinel-like composition and is particularly useful for gasoline enginesand/or diesel engines operated on a lean mixture. Among other things,the catalyst has a high resistance to substances present in the exhaustgas. Furthermore, the catalyst acts in an oxidizing manner with carbonmonoxide and hydrocarbons and in a reducing manner with NO_(x),particularly with NO and NO₂.

It is an object of the present invention to improve the method as wellas the purification device to improve the purifying effect during thestarting phase.

According to the present invention, this and other objectives areaccomplished by a method comprising the steps of

at temperatures below the response temperature of the catalytic materialcontained in the purification device, particularly at temperatures below200° C. and preferably at temperatures below 150° C., storinghydrocarbons present in the gas in the filter body,

at temperatures above the response temperature, releasing thehydrocarbons and

catalytically converting pollutants with the support material of thefilter body.

The present invention furthermore relates to a purification devicecomprising a filter body of catalytic material which stores at least 20%by volume, preferably at least 50% by volume, of hydrocarbons attemperatures below the response temperature of the catalytic material,particularly at temperatures below 200° C., preferably below 150° C.,wherein the catalytic material, with the help of a reducing agent whichis preferably hydrocarbon and/or carbon monoxide, catalytically reducespollutants.

By using a catalytically-active support material, which also acts as astorage medium for hydrocarbons at temperatures below the catalyticresponse temperature of the purification device, that is, at thetemperature at which the catalytic reduction and/or oxidation ofpollutants, particularly the catalytic reduction of NO_(x) and thecatalytic oxidation of CO takes place, it is possible to eliminateheating of the catalyst in the starting phase. Furthermore, hydrocarbonspresent in the exhaust gas can also be used as a reducing agent for thenitrogen oxides, especially for NO and NO₂, as a result of which theamount of these gases in the exhaust gas can be lowered. Moreover,because of the catalytic activity of the support material, the need forexpensive catalysts, such as noble metals, rare earth metals,lanthanide, etc. can be reduced as a result of which the purificationdevice becomes less expensive.

These and other objects, features and advantages will become moreapparent from the following detailed description of presently preferredembodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a purification device with a porous filter body made of thecatalyst and having an addition channel for a reducing agent;

FIG. 2 shows a purification device with a mechanism to supply reducingagent, which is disposed upstream of the filter body;

FIG. 3 shows a purification device with a mechanism with a nozzle ringfor supplying the reducing agent;

FIG. 4 is a graph of NO_(x)/CO₂ as a function of the temperature of aCuAl₂O₄ spinel-containing catalyst;

FIG. 5 is a graph of NO_(x)(NO) reduction and CO oxidation as a functionof the temperature of a Mg_(0.5)Cu_(0.5)Al₂O₄ spinel-containingcatalyst;

FIG. 6 is a graph of NO_(x)(NO) reduction and CO oxidation as a functionof the temperature of a catalyst which contains 20% ZnO, 16% CuO and 64%Al₂O₃, has a spinel structure and is additionally impregnated with 1.6%by weight of CeO₂;

FIG. 7 is a graph of NO_(x)(NO) reduction and CO oxidation as a functionof the temperature of a catalyst which contains 20% ZnO, 16% CuO and 64%Al₂O₃, has a spinel structure and is additionally impregnated with 8% byweight of CeO₂;

FIG. 8 is a graph of NO_(x)(NO) reduction and CO oxidation as a functionof the temperature of a catalyst which contains 20% ZnO, 16% CuO and 64%Al₂O₃, has a spinel structure and is additionally mixed with a solidcontaining WO₃, V₂O₅ and TiO₂;

FIG. 9 is a graph of NO_(x)(NO) reduction and CO oxidation as a functionof the temperature of a catalyst which contains 20% ZnO, 16% CuO and 64%Al₂O₃, has a spinel structure and additionally has 0.1% by weight ofvanadium; and

FIG. 10 is a graph of NO_(x)(NO) reduction and CO oxidation as afunction of the temperature of a catalyst which contains 20% ZnO, 16%CuO and 64% Al₂O₃, has a spinel structure and additionally has 0.5% byweight of palladium.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a purification device, comprising a porous filter body 2installed in the exhaust line 9 of a gasoline engine of a passenger car,for example. The filter body 2 has flow ducts 4 through which theexhaust gas, which is to be purified, flows and which are shown here aslinear ducts for clarity of illustration.

The exhaust gas which flows through the flow ducts 4, containshydrocarbons which can function as reducing agents for nitrogen oxideswhich are also present in the exhaust gas, and are generally NO and NO₂.However, after a certain treatment point, the hydrocarbons are consumedso that the filter body 2 no longer has any catalytic effect on thepollutants.

So that a further reduction of pollutants within the filter body 2 ofthe purification device is possible, the filter body 2, which is made ofthe catalyst, has an addition duct 3 for supplying reducing agentsbetween two flow ducts 4. The addition duct 3 is connected with thereservoir of a supplying mechanism, which is not shown. Preferably, theaddition duct 3 is connected with suitable safety measures to the tankventing system of the motor vehicle, so that the vapor space of the tankforms the reservoir.

Viewed in the flow direction 1 of the exhaust gas, the blind additionduct 3 is closed off on the gas inflow side and connected with thereservoir on the gas outflow side. Ammonia and, in motor vehicles,hydrocarbons have proven to be preferred reducing agents.

To supply the reducing agent, the reducing agent enters from the gasoutflow side and diffuses through the porous filter body 2, which hascapillary action, into the flow ducts 4 and evaporates there. As aresult, the concentration of reducing agent is increased in the exhaustgas, which has already been partially purified.

The increase in the concentration of hydrocarbons which takes placewithin the filter body 2, causes the pollutants remaining in thepartially purified exhaust gas, to be further reduced during the flow ofthe exhaust gases through the filter body, as a result of which theexhaust gas is more completely purified in the purification device. Theconcentration of pollutants in the exhaust gas can also be decreased bylowering the concentration of carbon monoxide and/or hydrocarbons.

In order to avoid an excess amount of reducing agent, the supplyingmechanism has metering equipment (not shown), such as a volumetric pump,so that the addition of reducing agent can be accurately measured.

The addition duct 3 can also extend from the outer periphery of thefilter body 2, transversely to the flow direction 1 of the exhaust gas,up to the center of the filter body 2. This embodiment, which is notshown, has the advantage that, with a single addition duct 3, severalflow ducts 4 can simultaneously be affected with reducing agent.Moreover, the advantage with this preferred embodiment, is that theaddition duct or ducts 3 can be supplied with reducing agent in a simplemanner from the direction of the outer periphery of the filter body 2.

In the case of a porous filter body 2, the supplying mechanismadvantageously has nozzles, particularly in the form of a nozzle ring 6,which are disposed peripherally in the filter body 2, out of which thereducing agent can flow through the filter body 2, preferably at rightangles to the direction of exhaust gas flow 1. The preferably gaseousreducing agent is also transported through the pores of the porousfilter body 2 in the direction of the exhaust gas.

The reducing agent is advantageously added after a certain treatmentpoint, which corresponds to a limit point at which the filter body 2 nolonger has any catalytic effect due to consumption. The limit pointcorresponds to that segment, through which gas is flowing, after which,as seen in the flow direction 1, a decrease in saturation of thepollutants, particularly of the reduction of nitrogen oxide, begins inthe catalyst of the filter body 2.

In FIG. 2, another purification device is shown, in which a filter body2 is disposed in an exhaust line 9 of an internal combustion engine,such as a gasoline engine or a gasoline engine operating on a leanmixture.

The embodiment of FIG. 2 differs from the embodiment of FIG. 1 in thatthe supplying mechanism comprises an atomizing nozzle 5, which isdisposed upstream of the filter body 2 through which the exhaust gasflows. The atomizing nozzle 5 is provided to atomize the reducing agentand is sized so that the reducing agent is atomized in droplets of suchsize that a drop is completely vaporized in the filter body 2 only afterit has penetrated the filter body 2 to a certain depth which preferablycorresponds at least to the saturation point. This droplet size can, forexample, be empirically determined. The renewed addition of reducingagent within the filter body 2 therefore takes place through evaporationof the drop within the filter body 2.

A further preferred embodiment of a purification device is shown in FIG.3. In the embodiment of FIG. 3, the filter body 2 is divided into threeparts to form a filter cascade. The filter body segments 7, 7′, and 7″of the porous filter body 2, through which the exhaust gas flows, arespatially separated from one another and serially disposed in the flowdirection of the exhaust gas. The length of a filter body segment 7, 7′,or 7″, measured in the flow direction 1, appropriately corresponds tothe limit point of the catalyst of the filter body 2.

In spaces 8 and 8′, disposed between the partial bodies or partial bodysegments 7, 7′, and 7″ of the filter body 2, nozzles 5 and 6, whichbelong to the supplying mechanism, are disposed. In the first space 8, anozzle ring 6 is disposed at the periphery from which the flow ofreducing agent proceeds radially inwards. In the second space 8′, acentrally disposed atomizing nozzle 5 is arranged. The reducing agentflows into the respective space 8 or 8′ and mixes with the alreadypartially purified exhaust gas. The space 8 or 8′ can therefore also beregarded as a sort of mixing chamber. The exhaust gas, enriched withreducing agent in spaces 8 and 8′, is then supplied to the next filterbody segment 7′ or 7″ respectively, in order to further decrease theconcentration of pollutants.

In all of the embodiments, the catalyst is preferably aspinel-containing solid. Spinels are materials of the general chemicalformula A_(a)B_(b)O₄, which have, at least microscopically, acrystallographical or crystalline cubic lattice structure withface-centered oxygen ions with tetrahedral or octahedral gaps, in whichthe A particles and up to 50% of the B particles are arranged in thetetrahedral gaps and the remaining B particles are arranged in theoctahedral gaps, with a+b≦3, a>0 and b>0. The term A particle or Bparticle refers only to the crystallographic arrangement. According tothe present invention, substoichiometric compounds in which the B_(b)O₃functions as a matrix, which have characteristic spinel lines in theirX-ray spectra, and in which the spinel of the composition A_(a)B_(b)O₄is present in the B_(b)O₃ matrix, so that an A_(a(1−x))B_(b)O₄stoichiometry results, with a+b<3, a>0, b>0 and 0≦x<1, are also regardedas spinels. From a material point of view, the A and B particles can bedifferent from one another.

In another embodiment, the support material of the filter body (2)comprises a catalytically active and substoichiometric composition ofthe general chemical formula A_(a(1−x))B_(b)O₄ in a B_(b)O₃ matrix, inwhich the composition is a spinel or is spinel-like, and hascharacteristic spinel lines in its X-ray spectrum, with a+b<3, a>0, b>0and 0≦x<1.

In a preferred embodiment, the catalyst is a material of the chemicalformula A1_(a1(1−x))A2_(a2(1−x)B) _(b)O₄, in which A1 and A2 areparticles of the A group, with a1+a2+b≦3, with a1>0, a2>0, b>0 and0≦x<1.

In another preferred embodiment, the catalyst is a material of thechemical formula A1_(a1(1−x))A2_(a2(1−x))B₂O₄, wherein A1 and A2 areparticles of the A group, with the proviso that a1+a2≦1 with a1>0, a2>0and 0≦x<1.

In a further preferred embodiment, the catalyst is a material of thechemical formula A1_(0.5(1−x))A2_(0.5(1−x))B₂O₄, with 0≦x<1.

In the spinel, the A particle is at least one element of the A groupconsisting of Mg, Ca, Mn, Fe, Ni, Co, Cu, Zn, Sn and Ti and the Bparticle is at least one element of the B group consisting of Al, Ga,In, Co, Fe, Cr, Mn, Cu, Zn, Sn, Ti and Ni. However, it should be notedthat none of the elements Mn, Fe and Co, can simultaneously be an Aparticle and a B particle.

The following spinel-like compositions are preferred according to thepresent invention: (MgCu)Al₂O₄, (CuCu)Al₂O₄, (CuZn)Al₂O₄, (CoZn)CuAl₂O₄,mixtures of (ZnCu)Al₂O₄ with WO₃ and/or V₂O₅ and/or TiO₂ andparticularly Mg_(0.5)Cu_(0.5)Al₂O₄, Cu_(0.5)Cu_(0.5)Al₂O₄,Cu_(0.5)Zn_(0.5)Al₂O₄, Co_(0.25)Zn_(0.25)Cu_(0.5)Al₂O₄ or their mixtureswith 10% WO₃ and 6% V₂O₅ and/or 84% TiO₂ and/or Al₂O₃.

Moreover, it is preferable to provide these spinels with catalyticallyactive elements such as palladium, platinum, rhodium, ruthenium, osmium,iridium, rhenium and/or rare earth metals such as lanthanum and cerium,vanadium, titanium, niobium, molybdenum, tungsten and/or their saltsand/or their oxides.

Further preferred embodiments are shown in the following examples:

EXAMPLE 1

A copper/aluminum spinel impregnated with copper having the compositionCu_(0.5)Cu_(0.5)Al₂O₄, was used. The spinel was synthesized by themethod disclosed in Published German Patent DE 43 01 470.

FIG. 4 is a graph of the NO_(x)/CO₂ concentration as a function of thetemperature obtained using the copper-impregnated CuAl₂O₄ spinel. Themeasurements were taken with the temperature increasing as well asdecreasing, the conversion showing a hysteresis with respect to the COand NO_(x).

To carry out the measurements, a 10 gram fragment of copper-impregnatedCuAl₂O₄ spinel was transferred to a vertically oriented quartz reactorhaving a diameter of 20 mm and a height of approximately 500 mm, inwhich a gas-permeable sintered glass disk was placed in the middle toexpose the sample. The height of the bed was about 15 mm. A furnace wasdisposed around the quartz reactor which heated the middle part of thereactor over a length of about 100 mm at temperatures of up to 550° C.

A gas mixture which consisted of 1,000 ppm NO, 1,000 ppm propene and 10%oxygen, with the remainder being argon as a carrier gas, was passedthrough the catalyst at a space velocity of about 10000 per hour. Afterthe gas mixture passed through the reactor, the NO concentration wasmeasured with a gas detector, in which any NO₂ present was reduced in aconverter to nitric oxide NO before the measurement. Simultaneously,oxidation of hydrocarbons to carbon dioxide was observed by measuringthe carbon dioxide content with the gas detector.

The result of the measurements with the spinel are shown in the graph ofFIG. 4. The NO and CO₂ concentrations are plotted in ppm as a functionof the temperature, with the NO_(x) concentration and the CO₂concentration being indicated differently, by empty squares and solidrectangles, respectively. The graph shows a clear decrease in theNO_(x)(NO) concentration as the temperature increases. Thisconcentration reaches a minimum between about 276° C. and 294° C. andsubsequently rises again. For the copper-impregnated CuAl₂O₄, a drasticdecrease in the NO_(x) concentration is observed at a temperature above200° C., the hydrocarbons being simultaneously decomposed to carbondioxide, as shown by the increase in the CO₂ concentration. Thetemperature range at which reduction of the NO_(x) takes place, liesbetween 200° C. and 400° C., depending on the composition of thematerial.

Similar measurement methods were used for the subsequent examples.

EXAMPLES 2

A magnesium/copper/aluminum spinel having the compositionMg_(0.5)Cu_(0.5)Al₂O₄, was used as the spinel. The spinel wassynthesized by a method similar to the method disclosed in PublishedGerman Patent DE 43 01 470.

The NO concentration in ppm was plotted as a function of the temperaturein FIG. 5. FIG. 5 clearly shows that the NO concentration decreases withincreasing temperature, a minimum being reached at about 320° C.

EXAMPLE 3

A mixture of 20% ZnO, 16% CuO and 64% Al₂O₃, referred to as a ZnCuAl₂O₄spinel, was used in the following Examples 3 to 7. In Example 3, thespinel used was impregnated with 1.6% by weight of CeO₂.

The results of the measurements with the ZnCuAl₂O₄ spinel of Example 3are shown in the graph of FIG. 6. The NO and carbon dioxideconcentrations are plotted in ppm as a function of the temperature, withthe NO_(x) and carbon dioxide concentrations indicated by differentsymbols. The diagram clearly shows a decrease in the NO_(x)(NO)concentration as the temperature increases. This concentration reaches aminimum at about 430° C. and subsequently rises again. For the ZnCuAl2O₄spinel impregnated with 1.6% by weight of CeO₂, a drastic decrease inthe NO_(x) concentration is observed at a temperature above 150° C.,hydrocarbons being simultaneously decomposed to carbon dioxide, as shownby the increase in the carbon dioxide concentration. The temperaturerange which shows a reduction in NO_(x) lies between 150° C. and 500°C., depending on the composition of the material.

EXAMPLE 4

The above ZnCuAl2O₄ spinel, which additionally contained 8% by weight ofCeO₂, was used. This spinel was prepared from a ZnCuAl₂O₄ spinel whichwas impregnated with 8% by weight of CeO₂.

The result of the measurements with the ZnCuAl₂O₄ spinel of Example 4,which was impregnated with 8% weight of CeO₂, is shown in the graph ofFIG. 7. The graph in FIG. 7 shows a clear decrease in the NO_(x)(NO)concentration as the temperature increased. This concentration reaches aminimum at 300° C. and subsequently rises once again.

For the ZnCuAl2O₄ spinel with 8% by weight of CeO₂, a drastic decreasein the NO_(x) concentration was observed at temperatures above 200° C.,with hydrocarbons simultaneously being converted to carbon dioxide, asshown by the increase in the carbon dioxide concentration. Thetemperature range at which there is reduction of NO_(x), ranges from200° C. to 500° C., depending on the composition of the material.

EXAMPLE 5

A mixture of the above-mentioned ZnCuAl2O₄ spinel, with tungsten,vanadium and titanium oxides, was used as the catalytic filter material.The mixture contained 50% by weight ZnCuAl₂O₄ spinel, with the remaining50% by weight of the mixture being formed by 5% by weight WO₃, 3% byweight V₂O₅ and 42% by weight TiO₂.

The results of the measurements with the spinel of Example 5 are shownin the graph of FIG. 8, which indicates a clear decrease in theNO_(x)(NO) concentration as the temperature increases. The concentrationreaches a minimum at about 240° C. and subsequently rises once again.

For this mixture, a drastic decrease in the NO_(x) concentration wasobserved at temperatures above 150° C., with hydrocarbons simultaneouslybeing converted to carbon dioxide, as shown by the increase in thecarbon dioxide concentration. The temperature range at which there is areduction of NO_(x), ranges from 150° C. to 500° C., depending on thecomposition of the material.

EXAMPLE 6

The ZnCuAl2O₄ spinel described above, impregnated with 0.1% vanadium,was used as the catalyst material.

The results of the measurements with the spinel of Example 6 are shownin the graph of FIG. 9, which shows a clear decrease in the NO_(x)(NO)concentration as the temperature increases. The concentration reaches aminimum at about 300° C. and subsequently rises once again.

For the ZnCuAl2O₄ spinel with vanadium, a drastic decrease in the NO_(x)concentration was observed at temperatures above 170° C., withhydrocarbons simultaneously being converted to carbon dioxide as shownby the increase in the carbon dioxide concentration. The temperaturerange at which there is a reduction of NO_(x), ranges from 170° C. to500° C., depending on the composition of the material.

EXAMPLE 7

The ZnCuAl2O₄ spinel described above, impregnated with 0.5% palladium,was used as the catalyst material.

The results of the measurements with the spinel of Example 7 are shownin the graph of FIG. 10, which shows a clear decrease in the NO_(x)(NO)concentration as the temperature increases. The concentration reaches aminimum at about 280° C. and subsequently rises once again.

For the ZnCuAl2O₄ spinel with 0.5% by weight of palladium, a drasticdecrease in the NO_(x) concentration was observed at a temperature above180° C., with hydrocarbons simultaneously being converted to carbondioxide as shown by the increase in the carbon dioxide concentration.The temperature range at which there is a reduction of NO_(x), rangesfrom 180° C. to 500° C., depending on the composition of the material.

For all of the foregoing examples, the temperature range givenadvantageously lies approximately at the temperatures which can occur inan exhaust system of an internal combustion engine.

Since the spinels have a good response behavior at relatively lowtemperatures and, furthermore, exhibit good hydrocarbon storage behaviorbelow this response temperature, they are particularly suitable for useas the support material for a three-way HC and/or CO and/or NO_(x)exhaust gas catalyst for stoichiometrically operated internal combustionengines.

Further testing of this catalyst additionally revealed high stability inthe presence of NO_(x), H₂O, and CO₂.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample, and is not to be taken by way of limitation. The spirit andscope of the present invention are to be limited only by the terms ofthe appended claims.

What is claimed is:
 1. An engine exhaust gas purification device,comprising: a porous body of catalytic material disposed in an exhaustgas stream of an engine, wherein said porous body of catalytic materialis catalytically active above 200° C. to reduce pollutants in thepresence of a reducing agent, and said porous body of catalytic materialstores at least 20% by volume hydrocarbons below 200° C., wherein thecatalytic material is a material of the chemical formulaA1_(a1(1−x))A2_(a2(1−x))B_(b)O₄, wherein A1 and A2 are independentlyselected from Mg, Ca, Mn, Fe, Ni, Co, Cu, Sn and Ti, with a1+a2+b≦3,with a1>0, a2>0, b>0 and 0≦x<1, and B represents Al.
 2. The purificationdevice of claim 1, wherein the catalytic material has at leastmicroscopically a crystallographic or crystalline cubic latticestructure with face-centered oxygen ions and with tetrahedral andoctahedral gaps, wherein the at least one of A1 and A2 and up to 50% ofaluminum is disposed in the tetrahedral gaps and wherein the remainingaluminum is disposed in the octahedral gaps.
 3. The purification deviceof claim 1, wherein the catalytic material is a material of the chemicalformula A1_(a1(1−x))A2_(a2(1−x))B₂O₄, wherein A1 and A2 areindependently selected from Mg, Ca, Mn, Fe, Ni, Co, Cu, Sn and Ti, witha1+a2≦1, a1>0, a2>0 and 0≦x<1 and B represents Al.
 4. The purificationdevice of claim 1, wherein the catalytic material is a material of thechemical formula A1_(0.5(1−x))A2_(0.5(1−x))B₂O₄, wherein A1 and A₂ areindependently selected from Mg, Ca, Mn, Fe, Ni, Co, Cu, Sn and Ti, with0≦x<1 and B represents Al.
 5. The purification device according to claim1, wherein the porous body of catalytic material comprises a catalystcomprising at least one catalytically active element selected frompalladium, platinum, rhodium, ruthenium, osmium, iridium, rheniumlanthanum, cerium, vanadium, titanium, niobium molybdenum, tungsten,salts thereof and oxides thereof.
 6. The purification device of claim 1,wherein the catalytic material stores at least 50% by volume ofhydrocarbons below 200° C.
 7. An engine exhaust gas purification device,comprising: a porous body of catalytic material disposed in an exhaustgas stream of an engine, wherein said porous body of catalytic materialis catalytically active above 200° C. to reduce pollutants in thepresence of a reducing agent, and said porous body of catalytic materialstores at least 20% by volume hydrocarbons below 200° C., wherein thecatalytic material is selected from the group consisting of (MgCu)Al₂O₄,(CuCu)Al₂O₄, (CuZn)Al₂O₄, and (CoZn)CuAl₂O₄.
 8. An engine exhaust gaspurification device, comprising: a porous body of catalytic materialdisposed in an exhaust gas stream of an engine, wherein said porous bodyof catalytic material is catalytically active above 200° C. to reducepollutants in the presence of a reducing agent, and said porous body ofcatalytic material stores at least 20% by volume hydrocarbons below 200°C., wherein the catalytic material is a mixture of (ZnCu)Al₂O₄ with atleast one of WO₃, V₂O₅, or TiO₂.
 9. An engine exhaust gas purificationdevice, comprising: a porous body of catalytic material disposed in anexhaust gas stream of an engine, wherein said porous body of catalyticmaterial is catalytically active above 200° C. to reduce pollutants inthe presence of a reducing agent, and said porous body of catalyticmaterial stores at least 20% by volume hydrocarbons below 200° C.,wherein the catalytic material is selected from the group consisting ofMg_(0.5)Cu_(0.5)Al₂O₄, Cu_(0.5)Cu_(0.5)Al₂O₄, Cu_(0.5)Zn_(0.5)Al₂O₄,Co_(0.25)Zn_(0.25)Cu_(0.5)Al₂O₄ and mixtures of these compounds with 10%WO₃ and at least one of 6% V₂O₅, 84% TiO₂, or Al₂O₃.
 10. An engineexhaust gas purification device, comprising: a porous body of catalyticmaterial disposed in an exhaust gas stream of an engine, wherein saidporous body of catalytic material is catalytically active above 150° C.to reduce pollutants in the presence of a reducing agent, and saidporous body of catalytic material stores at least 20% by volumehydrocarbons below 150° C., wherein the catalytic material is a materialof the chemical formula A1_(a1(1−x))A2_(a2(1−x))B_(b)O₄, wherein A1 andA2 are independently selected from Mg, Ca, Mn, Fe, Ni, Co, Cu, Sn andTi, with a1+a2+b≦3, with a1>, a2>0, b>0 and 0≦x<1, and B represents Al.